Explosive device and method of using such a device

ABSTRACT

An explosive device ( 10 ) comprising: and explosive charge body ( 12 ) including an explosive charge and detonator ( 21 ); a housing ( 22 ) attached to the explosive charge body ( 12 ); and a length of electrical or non-electrical non-pyrotechnic firing line ( 26 ) having a first ( 28 ) and second end ( 32 ) the majority of which is stored within the housing so as to permit progressive removal from the housing on pulling the first end ( 28 ) thereof, and which is attached at the second end ( 32 ) to the detonator ( 21 ). The explosive device ( 10 ) can be used in a versatile manner for avalanche control, can allow a degree of positioning after initial deployment and provide safe operation yet is easily handleable, readily deployed and compact, and negates the hazards associated with the use of pyrotechnic delay fuze.

This invention relates to an explosive device and method of using such adevice of particular, but not exclusive, application to triggeringavalanches in a controlled manner.

Avalanches can present a serious danger to people and property whentriggered in an uncontrolled manner, whether by a natural cause such asthe weather conditions or unintentionally as a result of human activitysuch as skiing or climbing. It has therefore become an establishedpractice in many mountainous areas to maintain continuous programs ofavalanche control.

Control techniques can be separated into two main categories; passiveand active. Two examples of passive control include a preventativeapproach, with the construction of terraced steel barriers high on themountain slopes to pin the snow layers and prevent slippage, and aprotective approach, where massive ground based deflectors areconstructed on lower parts of the mountain to divert avalanche debrisfrom specific structures considered to be at risk. Active avalanchecontrol techniques form part of a carefully organized and continuousprocess of weather system surveillance, local condition forecasting anda range of practical procedures designed to induce controlled artificialavalanche releases.

This practice of regularly triggering small, controlled releases isintended to minimise the build up of snow in known start zones which, ifleft, would eventually release naturally. Such natural releases of largevolumes of snow can cascade to develop massive slides invariably causingextensive damage to services, infrastructure, property and people.People are injured and killed by avalanches every year, world wide.

This invention supports active methods of avalanche control and inparticular the use of explosives to stimulate artificial avalancherelease. Explosives are used extensively in this role and a wide rangeof delivery methods are employed to suit the prevailing operationalenvironment. Some of the more common delivery techniques are describedbelow.

Where start zones are inaccessible, the explosive charge can bedelivered to the slope in the form of a projectile fired from a gun ormortar system where the projectile explodes on or shortly after impact.Short ranges (2 to 5 km) can be covered by gas gun projector systemssuch as the nitrogen driven avalauncher, used extensively in the U.S.,Canada and Europe. Longer ranges demand high performance systems andmilitary artillery pieces typical of the 105 mm howitzer and 106 mmrecoilless rifles have been used in this role for many years. Accuracyremains a problem for both systems at the limits of their rangeperformance. However, the most significant problem with the military gunsystems currently in use is that the ammunition is now obsolete andageing.

Although older military ammunition fuzes detonate upon impact (butalmost certainly well below the surface in the case of snow pack), infact, proximity air bursts above the surface produce the most effectiveavalanche release performance. However, with gun fired projectiles thiscan only be achieved with electronic proximity burst fuzes. The cost ofsuch fuzing is both inhibitive and notoriously unreliable against light,dispersed mediums such as surface snow, the use of impact fuzingtherefore continues.

A more recent approach, developed primarily for protection of road andrail routes in remote areas, involves a fixed installation bolted intothe mountain side in close proximity to an avalanche start zone. Theapparatus, known by its commercial name as Gaz-Ex, consists of a largedivergent funnel down which a charge of inflammable gas is injected andignited using a remote ratio command fire management system. Theresultant shock wave emitted from the mouth of the funnel thenstimulates the controlled release of small avalanches, the frequencybeing dictated by a combination of local weather surveillance andavalanche forecasting techniques.

Where sites are particularly inaccessible, or have become so due toheavy snow fall or are unsuitable for the use of gun systems and/or theinstallation of Gaz-Ex systems, helibombing is often employed.Helibombing involves dropping a bag of commercial explosive composition,typically ANFO, into the avalanche start zone from a helicopter. Thecharge is detonated via a length of pyrotechnic delay fuze which isignited in the helicopter before release.

US-A-4,817,529 discloses a method for automatically positioning a blastcharge at a predetermined position end height above the snow surface toachieve an air burst from the explosive charge. The charge is suspendedbelow a small host. The hoist and charge assembly are attached to afixed steel cable winch system that traverses the hoist and chargeassembly across the slope to the desired firing position. The smallhoist is then issued with a command to lower the charge until a sensescontact with the snow, and raise it back to a pre-determined heightabove the snow surface. The charge is fitted with a pyrotechnic delayfuze with a long burn time to allow for the overall positioning sequenceto be completed prior to detonation. This fixed system is useful forslopes with a known line of trigger points.

Most areas in ski resorts are accessible, including the mountain peaks,and this accessibility enables explosive charges to be delivered orplaced by hand. The practice of hand charge operations is probably themost cast affective and extensively used method of avalanche control inmany ski resorts but is carries with it obvious hazards in poor weatherconditions. The hand charge is a relatively simple device consisting ofa lightly cased (cardboard) explosive charge detonated by a length ofcapped pyrotechnic delay fuze. The fuze can either be ignited and thecharge thrown into a preferred position or the charge can bepre-positioned above the surface on a bamboo stick before the fuze isignited. In both cases, within the delay time, the operator must retireto a safe position before detonation occurs.

Perhaps the most undesirable characteristic of a pyrotechnic delay fuzeis that once the fuze has been ignited the only quick way to de-fuze thedevice is to attempt to cut the fuze beyond the flame front. This is notacceptable practice, but may be the only option when faced with anemergency. However, once ignited and abandoned, irrespective ofcircumstances, detonation of the charge cannot be evened. Thesecharacteristics together with the difficulty, in adverse weatherconditions, of detecting if a fuze has been properly ignited have led toinjury and fatalities in the past.

Not surprisingly, more appropriate firing systems have been adopted bythe majority of explosive user communities world wide. It is importantto recognize, however, that the particularly awkward range ofenvironmental conditions associated with avalanche control operationsimpose the continued use of pyrotechnic delay fuzes pendingidentification of a satisfactory alternative.

The present invention focuses on avalanche control operations using handcharges. It seeks to provide an explosive device which will extend theconvenience and versatility of hand charge control techniques.

The present invention, according to a first aspect, provides anexplosive device comprising: an explosive charge body including anexplosive charge and a detonator; a housing; and a length ofnon-pyrotechnic firing line having a first end and a second and, one endbeing operatively connected to the detonator, the majority of which lineis stored within the housing so as to permit progressive removal fromthe housing on pulling one of the ends thereof; and in which movement ofthe non-pyrotechnic firing line is restrained so as to prevent the oneend of the non-pyrotechnic firing line being pulled away from andoperatively disconnected from the detonator when the non-pyrotechnicfiring line is pulled from the housing.

The explosive charge of such a device can be launched towards a desiredsite while tethering the end of the non-pyrotechnic firing line notconnected to the detonator. The non-pyrotechnic firing line isrestrained from being pulled from the detonator as the non-pyrotechnicfiring line reaches its full extension. It also allows a degree ofrepositioning of the charge after initial charge deployment and providesinstantaneous control over the decision to detonate the charge. Theexplosive device remains easy to handle, readily deployable and compactand avoids the use of the pyrotechnic delay fuze component

The movement of the one end of the non-pyrotechnic firing line can berestrained by any convenient means, including for example, threading thenon-pyrotechnic firing line through one or more holes in the charge bodyproviding a tether between the non-pyrotechnic firing line and thecharge body or fixing the non-pyrotechnic firing line to the outside ofthe charge body by meant of a tape, adhesive or other convenientfastening or fixing means.

The non-pyrotechnic firing line can consist of two basic types, atwisted pair of electrical conductors for connection to an electricdetonator or a non-electric detonation transmission line. The latter isa known alternative initiation system to a slow-burn pyrotechnic fuze orelectrical conductor consisting of a non-pyrotechnic firing line offlexible plastics tube with a bore whose inner surface is coated with anexplosive composition. It is sometimes referred to as a “shook tube” asthe explosive coating is detonated at one end of the shock tube and adetonation shock front propagates down and is fully contained within itsinterior until it reaches, and so detonates, the reception compositionin the detonator cap.

Non-electric detonation transmission lines are preferred to avoid thehazards associated with inadvertent detonation due to strayradio-frequency fields.

The use of a non-pyrotechnic firing line means that it is known to theuser that there is no possibility of a late detonation in the event of amisfire. Further, the non-pyrotechnic firing line should be chosen to bestrong enough to support the weight of the charge ad it can be used toretrieve the explosive charge (typically about 1 kg in weight) in theevent of such a misfire or used to haul the device into a more preferredlocation prior to the final decision to detonate the charge.

By storing the rum-pyrotechnic firing line in a housing in the mannerdescribed, the explosive charge can be deployed in a variety of waysincluding throwing by hand or by a launcher or by hand placing theexplosive charge at the desired location and pulling the second end ofthe non-pyrotechnic firing line to a firing position.

The non-pyrotechnic firing line is preferably coiled within the housing,for example as a series of radially nested helices, to provide readypulling from the housing. Other storage layering can be used.

Conveniently, an end of the non-pyrotechnic firing fine is attached to atethering clip or tag to make it easier to grip in the hand or attachthe end to a fixed anchor.

The non-pyrotechnic firing line may extend from within the housing andbe fixed releasably to the outside of the housing or explosive chargebody for convenience of handling prior to use and readying the devicefor deployment.

The housing may comprise a thin sleeve which is a slide-fit over theexplosive charge body and retained in position by a strip of adhesivetape, but other means for storing the detonation transmission line inthe device ready for deployment may be employed.

Any conveniently available explosive charge may be used to constrict thedevice, particularly shaped charges, bare blast charges, or variousenhanced blast charge configurations.

In the letter two cases, the detonator may be embedded in the explosivecharge in a number of different positions to achieve different outputeffects. In the case of the simple bare blast charge the non-pyrotechnicfiring tine may be passed through the body of the explosive filling andpassed back into the detonator cap well.

An elongated support, normally bamboo, may be attached to the explosivecharge body to act as a standoff. Such a device may be used bypositioning the support in the snow so the explosive charge is fixed ina desired position and, if necessary, orientation. The free end of thenon-pyrotechnic firing line can then be pulled to the firing positionfrom where the charge can be detonated.

A second aspect of the present invention is method of using theexplosive device of the first aspect of the presets invention andcomprises deploying the device at or near a desired location with thenon-pyrotechnic firing line extending from the explosive charge to aninitiation site.

The method may also include the optional step of adjusting the positionand/or orientation of the device using the non-pyrotechnic firing fineprior to detonation and detonating the explosive charge.

The device may be hand-launched by the user or launched by anyconvenient launching device, such as a gas gun, riot gun or cross-bow.This allows the operator to stand well back from an unstable area duringthe placement operation.

In another method of use of the present invention, the explosive deviceis launched so the non-pyrotechnic firing line lies over a horizontalsupport, for example a cable, the vertical position of the device canthen be adjusted by pulling back the non-pyrotechnic firing line untilthe desired height above the snow is achieved.

Embodiments of the explosive device and methods of using such devices,all according to the present invention, will now be described, by way ofexample only, with reference to the accompanying drawings, of which:

FIGS. 1 to 2 are diagrammatic, cross-sectional views of two explosivedevices, each according to the present invention;

FIG. 3 is a photograph showing a hand thrown deployment of the explosivedevice of FIGS. 1 and 2;

FIGS. 4 and 5 are diagrammatic views of a number of hand-thrown orlaunched deployments of the explosive device shown in FIG. 1;

FIGS. 6 to 9 are diagrammatic views of further methods of deploying thedevice of FIG. 2 and

FIG. 10 is a diagrammatic, cross-sectional view of a further embodimentof the present invention.

Referring to FIG. 1, an explosive device 10 has an explosive charge body12. In this case a D90 hand charge manufactured by Dyno Nobel Americas,USA. It has an explosive charge 14 within a cylindrical case 16 cappedat one end by cap 18 having a bare explosive surface at the other. Adetonator 21 Is embedded in the charge 14.

A sleeve 22 of thin, waterproofed cardboard, a slide-fit over the case16, is retained in position on the charge body by a circumferentiallyextending strip of adhesive tape 24.

A 23 m length of 3 mm diameter non-pyrotechnic firing line 26 (in thiscase Nobel Dynoline shock tube) manufactured by Pro Nobel Americas, USA,is coiled within the housing 22 as a series of radially nested helices.Other lengths may be used as required, typically 18 to 30 m. A first end28 of the shock tube 26 extends from the last internal coil andterminates at an anti-snatch tag 28 to which it is secured. This firstend 28, when assembled, is located, for transit purposes, inside thespace within the shock tube coils. The second end 32 of the shock tube28 extends from the detonator 21 to a recess 34 in the charge near thecap 18 and then loops back towards the open end of the charge filling20. From there it passes radially outward to pass through a series ofcircumferentially spaced restraining holes 31 in the housing 22, beforelooping back into the interior of the housing 22 through hole 30 tostart the outer helix of the coiled shock tube 26.

The coiled shock tube assembly is a push-fit into the housing 22 but isretained within the housing by a ring 9 fixed to the open end of thehousing. The shock tube 26 is readily drawn from the housing 22 bypulling the tag attached to its first end 26 which can then be attachedto a fixed anchor, to the operator of to the launcher system beforelaunch of the complete assembly 10 to its desired location. The tag laoptional.

Referring now to FIG. 2, an explosive device is as that of FIG. 1 exceptthe bare blast charge body is replaced by a shaped charge explosive body40 of known type. Those parts in common with FIG. 1 have been given thesame reference numerals.

In this case the detonator is positioned on the axis at the open end ofthe charge 20 and the second end of the shock tube passes through aseries of restraining holes 46 in the casing 16 and aligned holes 31 inthe housing 22 before looping back through hole 30 in the housing 22 tothe interior of the housing 22.

It will be clear the present invention may be implemented using varioustypes of explosive bodies which can be detonated by use of an electricalor non-electrical non-pyrotechnic firing line.

FIG. 3 illustrates one example of a method of deployment of the deviceof FIG. 1. The first end 28 of the shock tube 26 is held by or attachedto the operator and the device 10 launched by hand, the shock tube 26being progressively pulled from the housing 22 of the device 10 duringthe flight of the device 10. An alternative method of launcheddeployment is to launch the device 10 using a mechanical or gas drivensystem whereupon a similar deployment of the shock tube 26 occurs. Theshock tube 26 binds on the restraining holes 31 when fully deployedpreventing the resultant “snatch” force being transmitted to the end ofthe shock tube connected to the detonator 21.

Once deployed the shock tube can be pulled to adjust the position and/ororientation of the device 10.

The device 10 can be launched or thrown so the shock tube 26 lies over ahorizontal support such as a cable 50 of a gantry 52, as shown in FIG.5, positioned at a desired location. The shock tube 26 can then be usedto lift the device to a desired position above the snow slab prior todetonation.

An example of hand-thrown or launched deployment of series of devices ofFIG. 1 is shown in FIG. 4. The devices 10 have been hung over the lineof a cornice build up, the shock tube 26 being used to set the depth ofoverhang of each charge before being tied off at the firing point. Thedetonators may embody different delays to provide successive detonationsfrom a single initiation stimulus provided from the firing point 41.Omnidirectional blast emission produced by the bare blast charge 10 isshown by “star” shaped area 64.

In all methods described in this application, the initiation can becarried out by a user using a handset or by means of a remote receiverof a radio command fire system 42, for example, located et the firingpoint 41.

FIGS. 6 to 8 illustrate an explosive device 60 which is as device 40 ofFIG. 2 but with a support stick 62 affixed to it so the device can bepositioned and orientated as required on a snow slab. The highly focusedblast emission produced by the enhanced blast charge 40 is shown by theextended “star” shaped area 65. They respectively illustrate the use ofthe device for cornice overhang removal with the device 60 providingcombined air shock and deep penetration, slab blasting with the deviceproviding combined air shock and deep penetration perpendicular to thesnow slab, and slab blasting where the device is orientated to providesuperficial disruption of the surface layer of a snow slab.

FIG. 9 shows a further embodiment of the present invention for cornicecontrol. The device 66 is as the device 40 but includes a conical endcap 68 to aid penetration into the soft back of the cornice followingremote delivery of the device from a short range launcher system.

FIG. 10 is a diagrammatic, cross-sectional view of a further embodimentof the present invention which has the same component parts as thedevice of FIG. 1 but the housing 22 has been rotated through 180° andthe first and second ends of the shock tube 26 are now connected to thedetonator 21 and tag 29, respectively.

The first end of the shock tube 26 is threaded through holes 46 tosecure it to the charge case 16, the second end is threaded throughholes 31 in the housing 22 to secure it to the housing 22.

This embodiment is used as follows. The explosive charge 12 is launchedby any suitable method, as the device of FIG. 1, but the housing 22 isretained at the launching point and the shock tube 26 pulled from thehousing 22 by the launched explosive charge 12. The tag 29 is againoptional and used to aid anchoring the second end, and in this case,also the housing 22, at the launch site.

Variations in design and method of use applicable to the carrierdescribed embodiments may also be adopted with this embodiment, so ashaped charge may be used.

What is claimed is
 1. An explosive device comprising: an explosivecharge body including an explosive charge and a detonator; a housing;and a length of non-pyrotechnic firing line having a first end and asecond end, one end being operatively connected to the detonator, themajority of which line is stored within the housing so as to permitprogressive removal from the housing on pulling one of the ends thereof;and in which movement of the no-pyrotechnic firing line is restrained soas to prevent the one end of the non-pyrotechnic firing line beingpulled away from and operatively disconnected from the detonator whenthe non-pyrotechnic firing line is pulled from the housing.
 2. Anexplosive device as claimed in claim 1, in which the non-pyrotechnicfiring line is coiled within the housing.
 3. An explosive device asclaimed in claim 2, in which the non-pyrotechnic firing line is coiledas a series of radially nested helices.
 4. An explosive device asclaimed is claim 1, in which the other end of the non-pyrotechnic firingline is attached to a tag.
 5. An explosive device as claimed in claim 1,in which the other end of the non-pyrotechnic firing line extends fromwithin the housing and is releasably fixed to the outside of the housingor explosive charge body.
 6. An explosive device as claimed in claim 1,in which the housing comprises a thin sleeve which is slide-fit over theexplosive charge body and, is retained in position by a strip ofadhesive tape.
 7. An explosive device as claimed in claim 1, in whichthe explosive charge is a shaped charge.
 8. An explosive device asclaimed in claim 1, in which the explosive charge is a blast charge. 9.An explosive device as claimed in claim 8 in which the detonator isembedded in the explosive charge and the non-pyrotechnic firing linefirst extends from the detonator away from the housing before it loopsback towards housing.
 10. An explosive device as claimed in claim 1,including an elongate support attached to the explosive charge body. 11.An explosive device as claimed in claim 1, in which the non-pyrotechnicfiring line is a non-electrical detonation transmission line.
 12. Anexplosive device as claimed in claim 1, in which either: a) thenon-pyrotechnic firing line is threaded through two or more holes in thecharge body; b) there is a tether connecting the non-pyrotechnic firingline to the charge body; or c) the non-pyrotechnic firing line is fixedto the outside of the charge body by means of adhesive tape, adhesive orother fastening or fixing means.
 13. A method of disturbing a snow orice formation using an explosive device comprising an explosive chargebody including an explosive charge and a detonator; a housing; and alength of non-pyrotechnic firing line having a first end and a secondend, one end being operatively connected to the detonator, the majorityof which line is stored within the housing so as to permit progressiveremoval from the housing on pulling one of the ends thereof; and inwhich movement of the non-pyrotechnic firing line is restrained so as toprevent the one end of the non-pyrotechnic firing line being pulled awayfrom and operatively disconnected from the detonator when thenon-pyrotechnic firing line is pulled from the housing, said methodcomprising deploying the explosive charge body at or near a desiredlocation with the non-pyrotechnic firing line extending from theexplosive charge to an initiation site and then detonating the explosivecharge.
 14. The method of claim 13 including adjusting the positionand/or orientation of the explosive charge body using thenon-pyrotechnic firing line and detonating the explosive charge prior todetonation of the explosive charge.
 15. The method of claim 13, in whichthe explosive charge body is hand-launched by the user to deploy theexplosive charge body.
 16. The method of claim 13, in which theexplosive charge body is launched by a launching device to deploy theexplosive charge body.
 17. The method claimed in claim 13, wherein theother end of said non-pyrotechnic firing line is attached to a tag, andin which the tag is attached to an anchor.
 18. The method claim 14 inwhich the explosive charge body is launched so the non-pyrotechnicfiring line lies over a support, and the step of adjusting the positionof the explosive charge body includes pulling the non-pyrotechnic firingline until the device is at a desired height above the snow.
 19. Themethod as claimed in claim 13 wherein said explosive device includes anelongate support attached to the explosive charge body, said methodfurther comprising: positioning the support in the snow so the explosivecharge body is in a desired position and orientation; pulling the otherend of the non-pyrotechnic firing line to firing position; anddetonating the explosive charge.
 20. The method of claim 19 wherein theother end of said non-pyrotechnic firing line is attached to a tag, andthe tag is attached to an anchor carried by the user and thenon-pyrotechnic firing line is pulled from the housing by the usermoving away from the device.
 21. The method as claimed in claim 15, inwhich the housing is retained at the launch site and the non-pyrotechnicfiring line is pulled from the housing by the explosive charge body whenlaunched.